Liquid toner clean-off system for high speed operation

ABSTRACT

When an electrostatic latent image on a record medium is developed using liquid toner, excess toner is left on the record. The excess toner is removed by passing the record over a toner clean-off head having an elongated opening extending across the record and maintained at reduced pressure. The maximum record velocity, at which satisfactory toner removal is obtained, is increased by proportioning the trailing land adjacent to the opening to promote high velocity air leakage between the land and the record into the opening. A further, substantial increase is obtained by orienting the clean-off opening so that the length thereof forms an oblique angle with the direction of record motion. Preferably, the angle is less than 30*. The clean-off opening may be broken into a plurality of shorter, intersecting openings arranged in a zig-zag pattern across the record, thereby reducing the space occupied along the length of the record.

United States Patent [151 3,654,659 [4 1 Apr. 11, 1972 Blumenthal [541 LIQUID TONER CLEAN-OFF SYSTEM FOR HIGH SPEED OPERATION [72] Inventor: John Blumenthal, Wickliffe, Ohio [73] Assignee: Clevite Corporation [22] Filed: May 6, 1970 [21] Appl. No.: 35,092

[52] US. Cl. ..15/306 A [51] Int. Cl. ..A47l 5/38 [58] Field of Search ..15/30l303, 306-311,

[56] References Cited UNITED STATES PATENTS 1,236,359 8/1917 Reynolds ..15/306 A UX 1,501,179 7/1924 Peacock et a1 ..15/302 X 1,908,284 5/1933 Butcher et a1. ..15/307 2,003,397 6/1935 Smith, Jr ..15/306 A 3,274,636 9/1966 MacGregor ..15/306 A 1,196,437 8/1916 Doyle ..15/306 A X 2,404,873 7/1946 Winkley... ..34/160 X 2,402,545 6/1946 Frum ..34/160 3,359,648 12/1967 Overly et al. ..34/160 Primary Examiner-Walter A. Scheel 7 Assistant Examiner-C. K. Moore Attorney-Eber J. Hyde 57 ABSTRACT When an electrostatic latent image on a record medium is developed using liquid toner, excess toner is left on the record. The excess toner is removed by passing the record over a toner clean-off head having an elongated opening extending across the record and maintained at reduced pressure. The maximum record velocity, at which satisfactory toner removal is obtained, is increased by proportioning the trailing land adjacent to the opening to promote high velocity air leakage between the land and the record into the opening. A further, substantial increase is obtained by orienting the clean-off opening so that the length thereof fonns an oblique angle with the direction of record motion. Preferably, the angle is less than 30. The clean-01f opening may be broken into a plurality of shorter, intersecting openings arranged in a zig-zag pattern across the record, thereby reducing the space occupied along the length of the record.

5 Claims, 6 Drawing Figures PATENTEDAPR 11 I972 SHEEI 1 UF 3 INVENTOR. JOHN BLUMENTHAL fl w ATTORNEY PATENTEDAPR 1 1 I972 SHEET 2 [IF 3 INVENTOR. JOHN BLUMENTHAL FIG.4

ATTORNEY PATENTEDAPR 11 m2 SHEET 3 [1F 3 FIG.6

INVENTOR. JOHN BLUMENTHAL ATTORNEY LIQUID TONER CLEAN-OFF SYSTEM FOR HIGH SPEED OPERATION BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to electrostatic image development by means of a liquid toner and, more particularly, to a system for removing excess toner from a developed record medium moving at relatively high velocity.

2. Description of the Prior Art An electrostatic printing system usually comprises means for creating an electrostatic latent image by selectively charging a suitable record medium, such as a web of electrically conductivized paper coated with a charge retentive dielectric layer, and a developer station where toner particles are attracted to the charged areas of the record medium. Development by means of a liquid toner, i.e., a liquid vehicle in which the toner particles are suspended, offers a number of advantages. Examples of liquid toning apparatus are found in U.S. Pat. No. 3,342,164 granted to Arthur M. Lewis, No. 3,41 1,482 granted to Ivor Brody, and No. 3,461,843 granted to Alonzo W. Noon.

1 have found that with liquid toning it is possible to develop a record medium moving at relatively high velocity, in excess of one hundred inches per second. However, when the velocity exceeds about ten to twenty inches per second, diffrculties are encountered in removing excess toner fluid left on the record medium and the results of high speed operation, therefore, have been less than satisfactory.

Accordingly, the object of this invention is to provide a system for removing excess toner fluid from a rapidly moving record medium that has been developed by the application of liquid toner.

SUMMARY OF THE INVENTION This invention provides a clean-off system for removing excess toner fluid from the surface of a rapidly moving record medium bearing an electrostatically formed image which has been developed by the application of liquid toner.

A clean-off head is provided which has an elongated opening bounded along one long edge by a first surface and bounded along the other long edge by a second surface having a relatively small area. The developed image bearing surface of the moving record medium engages the first surface and is closely adjacent to the second surface. The elongated opening is oriented so that the length thereof forms an oblique angle with the direction of motion of the record medium and so that the record medium approaches the opening over the first surface.

Suction means are provided for maintaining reduced pressure within the opening and for withdrawing from the opening the excess toner that is removed from the record medium into the opening.

The elongated opening may extend obliquely across substantially the full width of the record medium, or it may be broken into a plurality of shorter elongated openings disposed across the width of the record medium and arranged so that the areas of the record medium exposed to the plurality of openings overlap so that substantially the full width of the record medium experiences exposure to an opening as the record moves over the head.

Preferably, the angle between the length of each elongated opening and the direction of motion of the record medium is less than 30.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic, oblique view of an electrographic recorder employing a toner clean-off system according to this invention.

FIG. 2 is an isometric view of a portion of the toner cleanoff heads shown in FIG. 1.

FIG. 3 is an exploded view of the portion of the toner head of FIG. 2.

FIG. 4 is an isometric view of a portion of another form of toner clean-off head of this invention shown in engagement with a short section of record medium.

FIG. 5 is an exploded view of a portion of the toner cleanoff head of FIG. 4.

FIG. 6 is a side elevation of the head of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention will be described as it may be used in an electrographic recorder, but it should be understood that it is ap plicable wherever a latent image is impressed on a record medium by any means and subsequently developed by applying liquid toner.

In FIG. 1 the record medium 14 has a charge retentive surface 17 in engagement with an electrographic recording head 12 which may, for example, be constructed as described in my copending application Ser. No. 812,821, filed Apr. 2, 1969, and assigned to the same assignee as the present invention.

At charging head 12, the desired electrostatic latent image is impressed upon the charge retentive surface 17 of electrographic record medium 14.

The record medium 14 is transported, by conventional means not shown, in the direction of arrow 15.

At toner head 22, the electrostatic latent image is developed by liquid toner which is drawn by suction pump 23 from reservoir 25 through supply conduit 26 into the toner head. The depleted or partially depleted toner liquid is drawn from the toner head through conduit 28 to pump 23 and thence back to reservoir 25.

The toner head is not a part of this invention and, since such heads are well known in the art, further description is deemed to be unnecessary. In general, such toning heads, as well as all other liquid toning methods (e.g., immersion toning, spray toning), tend to leave an excess of liquid on the record medium and, for this reason, various means have been employed for removal of the excess, e.g., forced evaporation by heating, squeegeeing, etc. A simple vacuum cleaner" is effective at moderate record velocities. However, when the record medium is transported at relatively high velocity, for example, in excess of ten inches per second, prior art vacuum cleaners are inadequate for removal of excess toner.

In FIG. 1 an improved toner clean-off head or vacuum cleaner" is shown in conventional position (perpendicular to the direction of chart motion) at 29'. It may be constructed as shown in FIGS. 2 and 3. A body member 31 has a cavity 32 communicating with tubular member 34 which may be connected to suitable suction means such as pump 23. Cover 35 is spaced from body member 31 by shim 37 thereby forming an elongated suction opening 38 for removal of excess toner.

The record medium, after development at toner head 22, passes over surface 40 of the clean-off head, over suction opening 38, and finally over surface 41 of cover 35. Preferably, surface 40 has a relatively large area to minimize air leakage between that surface and the developed surface 17 of record 14 into suction slot 38.

On the trailing side of opening 38, it is desirable to have air leakage at high velocity. To achieve this, dimension (d) of land 41 (FIG. 3) is made very small. In an experimental head the surface at land 41 was reduced nearly to zero by beveling the cover to form a knife edge. When installed as shown at 29' in FIG. 1, toner clean-off was satisfactory at record velocities up to about forty inches per second.

For convenience and economy, it is desirable to have a welldeflned surfaceand this is achieved in the design of FIGS. 2

and 3 by milling away a portion of the upper edge of cover 35 to leave narrow land 41. Surface roughness and compliance of the record medium and the pressure drop across land 41 are factors that strongly influence the maximum allowable width of the land. Typically, useful widths range from 0.001 inch or less for a record medium with an extremely smooth surface to around 0.008 inch for a pebbled surface such as described in copending US. Pat. application Ser. No. 694,654, filed Dec. 29, 1967, in the names of Arling Dix Brown, Jr., and John Blumenthal, entitled Electrographic Record Medium, and assigned to the same assignee as the present invention.

For maximum clean-off effectiveness at high record velocity it is desirable to establish the largest practical pressure differential across the trailing land 41, i.e., to maintain the pressure within the clean-off head at or below one-tenth atmosphere. However, good results have been obtained at moderate velocity with pressure of about two-thirds atmosphere or about 5 psi below ambient pressure.

The dimensions of suction opening 38 are not critical. Where it engages the record, it should be narrow enough to prevent the chart from being sucked into the opening. Good results have been obtained with a slot width of about 0.03 inch. In the interior of the head, the opening should be large enough so that the resistance to air flow is much smaller than the resistance of the leak between chart and land 41.

A toner clean-off head, as described, and positioned as shown at 29 in FIG. 1, is adequate for moderate record velocities. With a sufficiently small land 41, good results have been obtained up to about forty inches per second, but this appears to be about the upper limit.

Excess toner may be removed at much higher record velocities by elongating the head and positioning it so that the length of the clean off opening forms an oblique angle 6 with the direction of record motion as shown at 29 in FIG. 1. The maximum record velocity at which satisfactory clean-off is obtained increases as the angle 0 is decreased. At an angle of 30, the maximum, satisfactory velocity is about doubled. At an angle of 11, satisfactory clean-off has been obtained at one hundred fifty inches per second and probably the limit is substantially higher. The experiment was limited by the speed of the available record drive system.

For convenience in describing the invention, I have shown in FIG. 1 two toner clean-off heads 29 and 29' with their outlets selectably connectable to suction pump 23 by two-way valve 30. Usually, in practice, only one clean-off head would be incorporated in a recorder, the position 29 or 29 being selected according to the maximum record velocity for which the recorder is designed.

As the angle between length of opening 38 and the direction of record motion is decreased, the length of the opening and, therefore, the length of the entire head must, of course, be increased in order for the head to be effective over the entire width of the record. In some cases, this may result in objectionable length for the entire apparatus, especially when designed for wide records.

I have found that the oblique clean-off opening may be broken into a plurality of shorter, intersecting openings disposed across the record medium in a zig-zag pattern as shown, for example, in FIG. 4, and this arrangement adds only slightly to the length of the apparatus.

In FIG. 4, leading surface 43 is in contact with the moving record medium 14. The vacuum slot 44 is in zig-zag form made up of branches 44-1, 44-2. These branches communicate with tubular member 46 and are connected at the ends so that the whole width of the record, except for the marginal edge, is exposed to suction as the record is transported across the head. Most of the remainder of the upper surface of the head is milled away at 47-1, 47-2 to leave a narrow zig-zag land 49 adjacent to the zig-zag opening 44. In operation, air enters between the record and the milled-away areas 47, and then flows over zig-zag land 49 at high velocity into zig-zag opening 44, stripping the excess toner from the record and carryin it into the opening 44. The performance of the cleanoff hea of FIG. 4 15 substantially the same as the performance of head 29 in FIG. 1 and occupies much shorter space in the direction of record motion.

The head of FIG. 4 may conveniently be constructed as shown in FIGS. 5 and 6. A shallow U-shaped frame 50 has a hole 52 through one end terminating in tubular member 46 for connection to a suction pump. The zig-zag opening and land are formed by assembling a plurality of blocks 55-1, 55-2 alternately within the frame 50. Each block 55 has a through hole 56 in alignment with hole 52 in the end of the frame 50. The suction openings 44-1, 44-2 forming the zig-zag opening are provided by making oblique saw cuts 58-1, 58-2 which intersect holes 56. The narrow trailing lands 49-1, 49-2 forming the zig-zag land are formed by milling away the surface to leave depressed areas 47-1, 47-2.

Alternate blocks 55-1, 55-2 are stacked in frame 50 and then clamped in place by screw 59 bearing on block 61 which has no hole or slot.

While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is aimed, therefore, in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. A toner clean-off system for removing excess liquid toner from the surface of a rapidly moving record medium bearing an electrostatically formed latent image which has been developed by the application of liquid toner, comprising:

a clean-off head having an elongated opening bounded along one long edge by a first surface in engagement with said surface of said moving record medium, and bounded along the other long edge by a second surface having a relatively small area adjacent to said surface of said moving record medium, said opening being oriented so that the length thereof forms an oblique angle with the direction of motion of the record medium and so that the record medium approaches said opening over said first surface; and

suction means for maintaining said opening pressure below ambient pressure and for withdrawing from said opening excess liquid toner removed from said record medium.

2. A toner clean-off system as described in claim 1 wherein said clean-off head has a plurality of elongated openings disposed across the width of the record medium in operatively intersecting relationship so that substantially the full width of the record medium is exposed to an opening as the record medium moves over said head and wherein said suction means is operative at each opening.

3. A toner clean-off system as described in claim 2 wherein said openings in said clean-off head are arranged in a zig-zag pattern, each opening communicating with an adjacent opening at an end thereof.

4. A toner clean-off system as described in claim 1 wherein the angle between the length of said opening and the direction of motion of said record medium is less than thirty degrees.

5. A toner clean-off system as described in claim 1 wherein the pressure within said opening is maintained at least five psi below ambient pressure. 

1. A toner clean-off system for removing excess liquid toner from the surface of a rapidly moving record medium bearing an electrostatically formed latent image which has been developed by the application of liquid toner, comprising: a clean-off head having an elongated opening bounded along one long edge by a first surface in engagement with said surface of said moving record medium, and bounded along the other long edge by a second surface having a relatively small area adjacent to said surface of said moving record medium, said opening being oriented so that the length thereof forms an oblique angle with the direction of motion of the record medium and so that the record medium approaches said opening over said first surface; and suction means for maintaining said opening pressure below ambient pressure and for withdrawing from said opening excess liquid toner removed from said record medium.
 2. A toner clean-off system as described in claim 1 wherein said clean-off head has a plurality of elongated opEnings disposed across the width of the record medium in operatively intersecting relationship so that substantially the full width of the record medium is exposed to an opening as the record medium moves over said head and wherein said suction means is operative at each opening.
 3. A toner clean-off system as described in claim 2 wherein said openings in said clean-off head are arranged in a zig-zag pattern, each opening communicating with an adjacent opening at an end thereof.
 4. A toner clean-off system as described in claim 1 wherein the angle between the length of said opening and the direction of motion of said record medium is less than thirty degrees.
 5. A toner clean-off system as described in claim 1 wherein the pressure within said opening is maintained at least five psi below ambient pressure. 